As is known in the art, a code is a rule for converting a piece of original information (for example, a letter, word, phrase, or other information) into another form or representation which may or may not necessarily be of the same type as the original information.
In the fields of communications and information processing, encoding and modulation is a process by which information from a source is converted into symbols to be communicated (e.g. transmitted via a transmitter). Decoding and demodulation is the reverse process, converting these code symbols back into information understandable by a receiver.
As is also known, an encoder is a device, circuit, process, processor, processing system or other system that converts information from one format or code to another. The process of encoding is often done for the purposes of reliability, error correction, standardization, speed, secrecy, security, and/or saving space.
As is also known, emerging technology and increasing demand for large-scale high-speed data communications have made it important for systems to achieve efficient and reliable digital data transmission. Strong error correction codes are necessary to fix errors introduced by noise and multipath fading in communication channels. For communication systems employing a single-transmitter, it is well known that turbo codes and low-density parity-check (LDPC) codes perform near Shannon capacity limits and that LDPC codes over binary field extensions outperform their binary counterparts.
Additionally, error correction coding is important for robust multiple-input multiple-output (MIMO) wireless communication systems. The use of multiple antennas increases system capacity and reliability when information symbols are appropriately coded and modulated across the multiple transmit antennas. Space-time modulation and coding research is a rich field covering areas such as orthogonal block codes, trellis codes, lattice codes, threaded codes, and algebraic codes. Recent works have also proposed using a non-binary Galois-field of size q [GF(q)] LDPC code in combination with a direct space-time modulation scheme. Their results show that for quasi-static channels of up to four transmit antennas, this coding and modulation combination performs within 0.5 dB of outage probability and 0.8 dB better than space-time bit-interleaved coded modulation with iterative detection (BICM-ID).
The appropriate coding rate to use for a system is dependent upon the communication channel. Time varying fading in the wireless channel between the transmitter and receiver antennas means that the maximum achievable data rate will change as the channel conditions vary or nodes are placed in different environments. Thus, a scheme is needed which effectively adapts data rate to the channel. Emerging wireless standards such as WiMAX, 802.11n, and Long Term Evolution (LTE) have proposed using different data rates to adapt to varying channel conditions. The number of different rates in such proposals, however, is limited because either different codes are needed for each rate or determining the rate adaptation scheme on a code for a given rate may not be easy. In addition, such schemes generally propose suboptimal rate adaptation techniques which result in performance loss as the rate is varied.